MBE GROWN ALUMINUM OXIDE AND ALUMINUM-GALLIUM OXIDE THIN FILMS FOR BETA-GALLIUM OXIDE POWER DEVICES

Abstract

β-Ga2O3 is a transparent conductive oxide and a relatively new member of the wide bandgap semiconductors family which has gained tremendous interest for power and RF electronics due to its ultra-wide bandgap, high breakdown field, and availability of high-quality cost-effective single-crystal wafers. The aim of this research is to use Molecular Beam Epitaxy (MBE) and explore the process conditions for growth of thin films related to β-Ga2O3 Metal Oxide Semiconductor Capacitor (MOSCAP) and Modulation Doped Field Effect Transistor (MODFET) device structures with excellent structural and electrical properties. The study of dielectrics and semiconductor/dielectric interfaces is critical for advancement of Ga2O3 devices research. The prospect of in-situ MBE grown aluminum oxide (Al2O3) dielectric for β-Ga2O3 based MOSCAPs is explored by comparing it against the conventional Atomic layer deposition (ALD) based Al2O3 dielectric. The properties of dielectric are shown to significantly depend on its crystallinity, morphology and density which in turn depend on the growth conditions. MBE grown Al2O3 dielectrics with properties comparable to their ALD based counterpart have been successfully achieved on (-201) oriented β-Ga2O3 substrates. The effect of substrate orientation, Al flux and post dielectric deposition annealing on properties of MBE grown Al2O3 dielectrics is also studied. This single chamber process of depositing metal/oxide/semiconductor structure could further enhance the promising electronic properties of β-Ga2O3 based devices. The study of β-Ga2O3 / (AlxGa1-x)2O3 heterostructure is of immense interest for the future of Ga2O3 MODFETs. The MBE process parameters are correlated to thegrowth rate, morphology, and Al composition and the various growth conditions of (AlxGa1-x)2O3 on (010) β-Ga2O3 substrates are explored. The effect of β-Ga2O3 substrate orientation on the structural properties of this heterostructure is also studied by comparing similar structures grown on (010) and (-201)oriented substrates. The resultant Ga2O3 / (AlxGa1-x)2O3 thin film with the highest quality can be doped to get the desired high electron mobility transistors.